Rubber crawler track

ABSTRACT

A rubber crawler track ( 1 ) has an endless rubber belt-shaped rubber crawler track main body ( 2 ) formed of a rubber elastic body and core metal pieces ( 3 ) embedded in the rubber crawler track main body ( 2 ) at predetermined intervals in a circumferential direction of the rubber crawler track, wherein a high hardness intermediate rubber layer track main body ( 2 ) is provided from below at least the ground contacting surface side of an end portion in a length direction (rubber crawler track width direction) of the core metal pieces ( 3 ) toward outside the end portion in a width direction of the rubber crawler track. The rubber elastic body of the rubber crawler track main body ( 2 ) is formed in a multiply layered structure with at least two or more layers.

TECHNICAL FIELD

The present invention relates to a rubber crawler track mounted on anendless track traveling device for farm working machines, constructionmachines, engineering work machines, and industrial vehicles such astransportation vehicles. Particularly, the present invention prevents alarge crack in the circumferential direction in the rubber crawler trackmain body in an end portion in a width direction of a rubber crawlertrack from occurring.

TECHNICAL BACKGROUND

Although an iron crawler track has been conventionally used as anendless track traveling device for mobile construction machine vehiclesand so on, it has recently come to be used in work on pavement in townareas. Therefore, a link-type rubber crawler track or an integral rubbercrawler track is used with the iron crawler track. Here, the link-typerubber crawler track is so constructed that backing shoes having rubberelastic bodies are integrally cured and bound on metallic shoe platesinstead of the iron crawler track, or rubber pads having rubber elasticbodies are directly cured and bound on exclusive core metal piecesinstead of the metallic shoe plates being mounted on a link comprising aplurality of endlessly-connected track links. Besides, the integralrubber crawler track comprises rubber pad shoes detachable on themetallic shoe plates of the iron crawler track, a tensile strengthlayer, core metal pieces embedded in an inside circumference of thetensile strength layer at predetermined intervals, and core metal pieceguide protrusions for preventing the crawler track from coming off outof the traveling device. The tensile strength layer is so constructedthat a plurality of tensile strength materials are arranged and embeddedin an endless rubber crawler track main body formed of a rubber elasticbody shown in FIG. 13 within a width direction of a rubber crawler trackalong its circumferential direction to form tensile strength materialrows. The core metal piece guide protrusions are formed so as to projecttoward the inside circumference of the rubber crawler track. Besides, arubber pad is made in a unit type of a track link length or a continuoustype of a length over a plurality of links.

When the conventional rubber crawler track is used in narrow places, onrough ground with many stones, or around a curb in a shoulder of a road,it runs aground on the stones, obstacles, and the curb (FIG. 14A), or ispressed in a lateral direction (FIG. 14B). Therefore, a rubber elasticbody put between an end portion of a crawler track width direction in acore metal piece limb embedded in the rubber crawler track and thestones and so on is deformed greatly. Therefore, the rubber elastic bodyis broken. Whenever such a state is repeated, destruction of the rubberelastic body progresses, thereby finally causing a large crack in thecircumferential direction in the rubber crawler track main body.

Some inventions have been proposed to prevent a large crack fromoccurring in the circumferential direction in the rubber crawler trackmain body.

For example, an invention for preventing a large crack from occurring inthe circumferential direction in the rubber crawler track main body bybending an end portion of a crawler track width direction in a coremetal piece limb toward the inside circumference (the groundnot-contacting surface) is disclosed in Japanese Patent No. 3077064,Japanese Patent Laid-open Publication Nos. 1999-079015 and 2000-313373.Besides, an invention for preventing a large crack from occurring in thecircumferential direction in the rubber crawler track main body bycurving an end portion of a crawler track width direction in a coremetal piece limb toward the inside circumference (the groundnot-contacting surface) is disclosed in Japanese Patent Laid-openPublication No. 1999-268673.

Besides, in Japanese Patent Laid-open Publication No. 1999-105754, anend portion of a crawler track width direction in a core metal piecelimb is formed in a round rib configuration to reduce the occurrence ofa large crack in the circumferential direction in the rubber crawlertrack main body.

However, in the above-mentioned inventions, the cost can not beprevented from being raised because a core metal piece moldingconfiguration and processes for making core metal pieces, such as a coremetal piece finishing, are complicated in addition to the shape of thecore metal piece being complicated.

In addition, in Japanese Utility Model Laid-open publication No.1977-068532, a reinforcing rib is formed by increasing the thickness ofrubber of the ground contacting surface side corresponding to both endsof a crawler track width direction in a core metal piece limb to preventa large crack from occurring in the circumferential direction in therubber crawler track main body. Moreover, in Japanese Utility ModelLaid-open publication No. 1978-050935, a rubber crawler track has athick protrusive bar around an end portion of a crawler track widthdirection in a core metal piece.

However, in the above-mentioned invention, although rubber near the coremetal piece limb can be prevented from bending and deforming, rubberoutside (the ground contacting surface side) the reinforcing rib or thethick protrusive bar is easy to bend and deform. Accordingly, a largecrack in the circumferential direction in the rubber crawler track mainbody occurs on these portions, and an efficient improvement has not beenachieved yet.

Furthermore, in Japanese Patent No. 3077064, to prevent a large crackfrom occurring in the circumferential direction in the rubber crawlertrack main body, a cable layer is provided below the ground contactingsurface side of a portion of a crawler track width direction of a coremetal piece limb, and a synthetic resin material is arranged near theend portion of a crawler track width direction of a core metal piece.

In Japanese Laid-open Publication No. 2000-085642, a low frictionalresistive member is embedded in a taper portion of an end of a crawlertrack width direction in a rubber lug so that the surface is exposed.However, a large crack in the circumferential direction in the rubbercrawler track main body cannot be effectively and economically preventedby this method.

The present invention aims to settle the above-mentioned problems and toprovide a rubber crawler track capable of preventing a large crack fromoccurring in the circumferential direction in the rubber crawler trackmain body effectively and economically.

SUMMARY OF THE INVENTION

The present invention relates to a rubber crawler track having anendless rubber belt-shaped rubber crawler track main body formed of arubber elastic body, etc. and core metal pieces embedded in the rubbercrawler track main body at predetermined intervals in a circumferentialdirection of the rubber crawler track. And therein, a high hardnessintermediate rubber layer formed of a high hardness rubber elastic bodyhaving higher hardness than other rubber elastic bodies forming therubber crawler track main body is provided from below at least theground contacting surface side of an end portion in a length direction(rubber crawler track width direction) of the core metal pieces towardoutside an end portion in a width direction of the rubber crawler track.The present invention is characterized by the rubber elastic body of therubber crawler track main body being formed in a multiply layeredstructure with at least two or more layers.

In the rubber crawler track of the present invention, the core metalpieces embedded in the rubber crawler track main body have end portionsin the length direction (end portions of core metal piece limbs) withtips turned toward the ground contacting surface side to form downwardinclinations within a predetermined length.

Besides, the present invention is characterized by bulgy portionsarranged between rubber lugs in the circumferential direction of therubber crawler track. The bulgy portions are formed by suitably makingthick the rubber of the ground contacting surface side in the rubbercrawler track width direction, including portions corresponding to theend portions in the length direction of the core metal pieces (thethickness of a base rubber).

In the rubber crawler track of the present invention, since the highhardness intermediate rubber layer formed of the high hardness rubberelastic body having higher hardness than other rubber elastic bodiesforming the rubber crawler track main body is provided from below atleast the ground contacting surface side of the end portion in thelength direction of the core metal pieces toward outside the end portionin the width direction of the rubber crawler track, and the rubberelastic body of the rubber crawler track main body is formed in amultiply layered structure with at least two or more layers, when therubber crawler track runs aground on stones or curbs, strain occurringon the rubber elastic body of the rubber crawler track main body betweenthe end portions of the core metal piece limbs and the stones or thecurbs is effectively dispersed. Therefore, the strain is prevented fromconcentrating on a part, thereby preventing rubber destruction fromoccurring and effectively diminishing the occurrence of a large crack inthe circumferential direction in the rubber crawler track main body.Accordingly, the durability of the rubber crawler track can be improved.

Besides, in the present invention, a large crack in the circumferentialdirection in the rubber crawler track main body can be sufficientlyprevented by merely making a part of the rubber elastic body into theintermediate rubber layer having higher hardness than other rubberelastic bodies. Since it is unnecessary to use expensive materials (forexample, steel cords, etc.) that increase the material cost in additionto the complicated production process, a large crack in thecircumferential direction in the rubber crawler track main body can beprevented economically and effectively.

In this case, the intermediate rubber layer can be designed and used ina desirable optional combination of exclusive rubber.

In the second characterization of the present invention, the outsidecircumference (ground contacting surface side) of the rubber crawlertrack in the end portion in a length direction of the core metal pieceis formed in a downward inclination within a predetermined length towardthe ground contacting surface side. By this, the strain of the rubberbetween the end portions of the core metal piece limbs and the stones orthe curbs is prevented from concentrating on a part, thereby preventingthe rubber destruction from occurring and diminishing the occurrence ofa large crack in the circumferential direction in the rubber crawlertrack main body.

Since the core metal pieces are merely provided with inclinations on theend portions of their limbs in comparison with the conventional oneswhose end portions of the length direction are bent to an insidecircumferential side, the improvement of the shape can be simplyachieved. Therefore, the cost is not increased. Here, the inclination ofthe end portion of the length direction of the core metal piece may be aconvex curved surface.

In the third characterization of the present invention, the thickness ofthe ground contacting surface (the outside circumference) side of therubber crawler track in the end portion of the rubber crawler trackwidth direction including the portion corresponding to the end portionof the length direction of the core metal piece is made suitably thick,and the bulgy portion is arranged between the rubber lugs thereof. Bythis, the rigidity of the end portions in the width direction of rubbercrawler track is increased. When the rubber crawler runs aground on oris pressed against the stones or the curbs, the end portions of thewidth direction of the rubber crawler track turn to be difficult to bebent to the inside circumferential side (ground not-contacting surfaceside). When the end portions of the width direction of the rubbercrawler track are bent to the inside circumferential side, the strain ofthe rubber elastic body corresponding to the end portions of the lengthdirection of the core metal piece can be reduced. Therefore, theoccurrence of a large crack in the circumferential direction in therubber crawler track main body can be reduced.

Besides, in the rubber crawler track combining the above-mentionedfeatures, the ability for preventing a large crack from occurring in thecircumferential direction in the rubber crawler track main body isbetter than for the conventional method. Therefore, the durability ofthe rubber crawler track can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 show a rubber crawler track of the first embodiment. FIG. 1A is aplan view of the inside circumferential side (ground not-contactingsurface side), FIG. 1B is a plan view of the outside circumferentialside (ground contacting surface side), and FIG. 1C is a sectional viewin a width direction of the rubber crawler track.

FIG. 2 is an enlarged view of an important part of FIG. 1C.

FIG. 3 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler track showing another example of the firstembodiment.

FIG. 4 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler track showing a further example of thefirst embodiment.

FIG. 5 is a sectional view in a width direction of a rubber crawlertrack of a second embodiment.

FIG. 6 show a core metal piece embedded in a rubber crawler track mainbody of the second embodiment. FIG. 6A is a plan view of the insidecircumferential side (ground not-contacting surface side), FIG. 6B is aplan view of the outside circumferential side (ground contacting surfaceside), FIG. 6C is a front view, and FIG. 6D is a side view.

FIG. 7 is an enlarged sectional view of an important part of a rubbercrawler track of a third embodiment.

FIG. 8 show a rubber crawler track of a fourth embodiment. FIG. 8A is aplan view of the outside circumferential side (ground contacting surfaceside), FIG. 8B is a plan view of the inside circumferential side (groundnot-contacting surface side) and FIG. 8C is a sectional view in a widthdirection of the rubber crawler track.

FIG. 9 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler of a fifth embodiment.

FIG. 10 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler of a sixth embodiment.

FIG. 11 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler of another example of the sixthembodiment.

FIG. 12 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler of a seventh embodiment.

FIG. 13 is a sectional view in a width direction of a rubber crawlertrack showing a conventional rubber crawler track.

FIG. 14A is a sectional view in a width direction of a rubber crawlertrack, in a first situation that produces a large crack in thecircumferential direction in the rubber crawler track main body in aconventional rubber crawler track; and FIG. 14B is a sectional view in awidth direction of a rubber crawler track in a second situation thatproduces a large crack in the circumferential direction in the rubbercrawler track main body in a conventional rubber crawler track.

FIG. 15 is a sectional view of a width direction of a conventionalrubber crawler that takes measures to cope with a large crack in thecircumferential direction in the rubber crawler track main body.

FIG. 16 is a diagram showing an examination result regarding aperformance test concerning resistance to a large crack forming in thecircumferential direction in the rubber crawler track main bodycomparing the present invention with a conventional product.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereafter, embodiments of the present invention will be described withreference to the drawings.

FIG. 1A is a plan view of the inside circumferential side (groundnot-contacting surface side) of a rubber crawler track of the firstembodiment of the present invention. FIG. 1B is a plan view of theoutside circumferential side (ground contacting surface side). FIG. 1Cis a sectional view in a width direction of FIG. 1B. FIG. 2 is anenlarged view of an important part of FIG. 1C.

A rubber crawler track 1 of the first embodiment comprises an endlessrubber belt-shaped rubber crawler track main body 2 formed of a rubberelastic body, etc. and core metal pieces 3 embedded therein atpredetermined intervals in a circumferential direction. Rubber lugs 4are protrusively formed on the ground contacting surface side of therubber crawler track 1. Steel cord rows 6 are embedded on the outsidecircumferential side of the core metal pieces 3 along thecircumferential direction of the rubber crawler track so as to bedivided to the left and right of engaging holes 5 that interlock with adriving wheel of a travelling device. A rubber elastic body covering anend portion 3 a′ of a limb 3 a of a core metal piece 3 is made inthree-layers, comprising an outside rubber layer 7 a, an intermediaterubber layer 7 b and an inside rubber layer 7 c. The intermediate rubberlayer 7 b is harder than the outside rubber layer 7 a and the insiderubber layer 7 c. Accordingly, when the rubber crawler track runsaground on stones or a curb, strain occurring on the rubber elastic bodybetween the end portion 3 a′ and the stones or curb is dispersed by thehigh hardness intermediate rubber layer 7 b. Therefore, the strain isprevented from concentrating on a part and the rubber elastic body isnot broken, thereby preventing a large crack from occurring in thecircumferential direction in the rubber crawler track main body.

Besides, in the first embodiment, the rubber hardness (JIS K6253:1997;Durometer A hardness) of the outside rubber layer is 69 degrees, that ofthe intermediate rubber layer is 85 degrees, and that of the insiderubber layer is 69 degrees. The thickness of the intermediate rubberlayer is 6 mm. In the present embodiment, although it is clearly statedthat the outside rubber layer is different from the inside rubber layer,for convenience' sake, in the first embodiment, they are formed of arubber elastic body with the same rubber hardness and the same rubbercompound. Accordingly, if the outside rubber layer and the inside rubberlayer are regarded as the same layer, the present embodiment is formedin a two-layer structure.

In the above-mentioned embodiment, although the rubber hardness (JISK6253:1997; Durometer A hardness) of the intermediate rubber layer isharder than those of the outside rubber layer and the inside rubberlayer by 16 degrees, it is not limited to this in the present invention.In the case of a rubber crawler track being used under normalconditions, the rubber hardness of the intermediate rubber layer may beharder than those of the outside rubber layer and the inside rubberlayer by 16 degrees at least over 4 to 7 degrees of Durometer Ahardness.

In this case, when the rubber hardness (JIS K6253:1997; Durometer Ahardness) of the intermediate rubber layer is over 95 degrees, theflexibility of the rubber elastic body goes down, thereby causing earlyflexing fatigue and decreasing durability. Therefore, it is notpreferable to use a high hardness rubber elastic body having a hardnessmore than this.

Accordingly, the rubber hardness (JIS K6253:1997; Durometer A hardness)of the outside rubber layer or the inside rubber layer is set up withinthe range of 50 degrees to 90 degrees, which is the same range as theconventional rubber crawler track. The intermediate rubber layer isformed of a rubber elastic body harder than the outside rubber layer andthe inside rubber layer by at least more than 4 degrees of Durometer Ahardness. And it is preferable that the upper limit of the rubberhardness (JIS K6253:1997; Durometer A hardness) is about 95 degrees.Usually, the rubber hardness of the rubber elastic body might just aswell be set up within the range of 54 degrees to 95 degrees of DurometerA hardness. The hardness of each rubber layer, the number of layers andthe thickness of the layer are decided in accordance with the weight ofa vehicle and a machine, specification and the requisite durability, andbesides, may be suitably designed in consideration of the material ofthe rubber due to the combination of the rubber in the rubber elasticbody. The hardness need not be always within the above-mentioned range.

FIG. 3 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler track showing another example of the firstembodiment.

FIG. 3A shows a rubber crawler track 1 of another example wherein theintermediate rubber layer 7 b extends to a side end portion 2 a thereof.The intermediate rubber layer 7 b is formed of a high hardness rubberelastic body covering an end portion 3 a′ of the core metal piece limb,and divided into an inside circumferential side and an outsidecircumferential side with respect to the crawler track in a verticaldirection. Here, the high hardness intermediate rubber layer 7 b isarranged in a plurality of layers.

FIG. 3B shows a rubber crawler track of another example 2 wherein theintermediate rubber layer 7 b of the example 1 does not reach the sideend portion 2 a.

FIG. 4 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler track showing a further example of thefirst embodiment.

FIG. 4A shows a rubber crawler track of another example wherein theintermediate rubber layer 7 b of high hardness rubber elastic bodycovering the end portion 3 a′ of the core metal piece limb is providednear the underside of the ground contacting surface side of the rubbercrawler track in the vertical direction. In this case, the intermediaterubber layer 7 b extends to the side end portion 2 a of the rubbercrawler track.

FIG. 4B shows a rubber crawler track of another example wherein theintermediate rubber layer 7 b of the example of FIG. 4A does not reachthe side end portion 2 a.

FIG. 5 is a sectional view in a width direction of a rubber crawlertrack of a second embodiment. FIG. 6 show a core metal piece embedded ina rubber crawler track main body of the second embodiment. FIG. 6A is aplan view of the inside circumferential aide (ground not contactingsurface side), FIG. 6B is a plan view of the outside circumferentialside (ground contacting surface side), FIG. 6C is a front view, and FIG.6D is a side view.

A rubber crawler track 1 of the second embodiment is so constructed thatcore metal pieces 3 in FIG. 6 are embedded in the rubber crawler track 1of the first embodiment. Each core metal piece 3 includes an inclination3 b, by which end portions in a length direction of the core metal pieceare inclined toward the ground contacting surface side within a fixedlength.

In this embodiment, the rubber elastic body covering the end portion 3a′ including the inclination 3 b of the core metal piece limb is made ina three-layer structure comprising an outside rubber layer 7 a, anintermediate rubber layer 7 b and an inside rubber layer 7 c. Thehardness of the intermediate rubber layer 7 b is made to be higher thanthat of the outside rubber layer 7 a or the inside rubber layer 7 c.

Accordingly, strain imposed on the rubber elastic body by stones orcurbs is suitably dispersed by the high hardness intermediate rubberlayer covering the end portion 3 a′ of the core metal piece limb and theinclination 3 b thereof, thereby effectively preventing a large crackfrom occurring in the circumferential direction in the rubber crawlertrack main body. Therefore, the rubber crawler track can improve indurability.

FIG. 7 is an enlarged sectional view of an important part of a rubbercrawler track of a third embodiment.

Core metal pieces 3 embedded in the rubber crawler track 1 of the thirdembodiment are so constructed that each has an inclination 3 b formed onthe crawler track ground contacting surface side of the end portion 3 a′in FIG. 6 of the second embodiment.

In this embodiment, the intermediate rubber layer formed of the highhardness rubber elastic body does not lie within the rubber crawlertrack main body. Although the effect for preventing a large crack fromoccurring in the circumferential direction in the rubber crawler trackmain body is inferior to that of the second embodiment, an equal effectcan be gained according to the above-mentioned core metal pieces. Evenif the rubber crawler track 1 runs aground on the stones or the curbs,strain is not concentrated on a part of the rubber elastic body putbetween the end portion 3 a′ and them, and is effectively dispersed andlightened by the core metal piece shape. Therefore, a rubber elasticbody in this portion is not destroyed and the rubber crawler track canprevent a crack from occurring, thereby preventing a large crack fromoccurring in the circumferential direction in the rubber crawler trackmain body.

FIG. 8 show a rubber crawler track of a fourth embodiment. FIG. 8A is aplan view of the ground contacting surface side, FIG. 8B is a plan viewof the inside circumferential side (ground not contacting surface side)and FIG. 8C is a sectional view in a width direction of a rubber crawlertrack.

A rubber crawler track 1 of the fourth embodiment is so constructed thatbulgy portions 2 b are arranged between rubber lugs in a circumferentialdirection of the rubber crawler track, in addition to the structure ofthe rubber crawler track 1 of the first embodiment. Here, a bulgyportion 2 b is formed on the end portion in the crawler track widthdirection of the rubber crawler track. That is, the bulgy portion 2 b isformed by suitably increasing the rubber thickness (base thickness) ofthe ground contacting surface side of the rubber crawler track widthdirection, including a portion corresponding to the end portion of thecore metal piece limb.

According to this, the rigidity in the end portion of the rubber crawlertrack including the end portion 3 a′ of the core metal piece limb comesto be high. Even if the rubber crawler track runs aground on stones orcurbs, the end portions of the rubber crawler track are difficult tobend to the inside circumferential side of the crawler track.Accordingly, the end portions in the width direction of the rubbercrawler track are prevented from partially bending, the strain on therubber elastic body is decreased, and a large crack in thecircumferential direction in the rubber crawler track main body can beeffectively prevented.

FIG. 9 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler of a fifth embodiment.

In the rubber crawler 1 of the fifth embodiment, the core metal pieces 3of the third embodiment are embedded. And therein, the rubber thicknessof the rubber crawler track main body 2 including the portioncorresponding to the end portion 3 a′ of the core metal piece limbgradually increases toward the ground contacting surface side of avertical direction of the rubber crawler track. Besides, bulgy portions2 b are formed between lugs 4 in the end portions of the rubber crawlertrack.

According to this, the inclinations 3 b and the bulgy portions 2 b havethe strain dispersed more suitably on the rubber elastic body caughtagainst stones or curbs. Therefore, in the end portions of the rubbercrawler track, the degree of bending to the inside circumferential sideis decreased, partial bending is prevented, and cracks are preventedfrom occurring. Accordingly, a large crack in the circumferentialdirection in the rubber crawler track main body is effectively preventedfrom occurring when the rubber crawler track 1 runs aground on thestones or the curbs, thereby enabling the durability of the rubbercrawler track to improve.

FIG. 10 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler track of a sixth embodiment.

The rubber crawler 1 of the sixth embodiment is so constructed that thecore metal pieces 3 of the second embodiment are embedded in the rubbercrawler track 1 of the first embodiment, and bulgy portions 2 b areformed on the rubber crawler track main body.

That is, the inclinations 3 b are respectively provided on the groundcontacting surface side of the end portions 3 a′ of the core metal piecelimb 3 a embedded in the rubber crawler 1. Besides, the rubber elasticbody covering the end portions 3 a′ is formed in a three-layer structurecomprising an outside rubber layer 7 a, an intermediate rubber layer 7 band an inside rubber layer 7 c. Here, the rubber hardness of theintermediate rubber layer 7 b is higher than those of the outside rubberlayer 7 a and the inside rubber layer 7 c. Besides, the rubber thicknessof the end portion of the rubber crawler track including the portioncorresponding to the end portion 3 a′ of the core metal piece limbgradually increases toward the ground contacting surface side in thevertical direction of the rubber crawler track. And the bulgy portion 2b is formed between the lugs 4 of the end portion of the rubber crawlertrack.

In this embodiment, the rigidity of the rubber crawler track can improvebecause the ground contacting surface side of the rubber crawler trackincluding the portion corresponding to the end portion of the core metalpiece limb is made thick. Therefore, when the end portions of the rubbercrawler track run aground on stones or curbs, the end portion of therubber crawler track outside the tip of the core metal piece limb can beprevented from partially bending. Accordingly, the most suitable rubbercrawler track effectively preventing a large crack from occurring in thecircumferential direction in the rubber crawler track main body causedby the partial bending can be formed.

FIG. 11 are enlarged sectional views of an important part in a widthdirection of a rubber crawler track showing other examples of the sixthembodiment.

In an example shown in FIG. 11A, the rubber elastic body of theintermediate rubber layer 7 b in the sixth embodiment is divided into aninside circumferential side and an outside circumferential side withrespect to the vertical direction of the rubber crawler track to arrangea double-layer intermediate rubber layer. Here, the rubber elastic bodyof the intermediate rubber layer 7 b extends to the end portion 2 a ofthe rubber crawler track width direction.

In another example shown in FIG. 11B, the intermediate rubber layer 7 bdivided into a top and bottom in the example of FIG. 11A forms a largelayer at the end portion of the rubber crawler track.

FIG. 12 is an enlarged sectional view of an important part in a widthdirection of a rubber crawler track of a seventh embodiment.

The rubber crawler track in the seventh embodiment comprises the outsiderubber layer 7 a, the intermediate rubber layer 7 b and the insiderubber layer 7 c with different configurations and hardness,respectively.

In particular, the intermediate rubber layer 7 c is formed of a rubberelastic body in consideration of adhesion to the core metal piece (steeletc.), and the outside rubber layer 7 a is formed of a rubber elasticbody superior in cutting resistance and is difficult to be externallydamaged.

The rubber hardness (JIS K6253:1997; Durometer A hardness) of theoutside rubber layer 7 a in this embodiment is 66 degrees, that of theintermediate rubber layer is 83 degrees, and that of the inside rubberlayer is 70 degrees.

According to this embodiment, the adhesive portion between the tip ofthe core metal piece limb and the rubber elastic body caused by the bendof the end portion of the rubber crawler track generated when the rubbercrawler track runs aground on stones or a curb or is pressed againstthem is prevented from peeling. Besides, a large crack in thecircumferential direction in the rubber crawler track main body causedby this is also prevented from occurring.

Table 1 in FIG. 16 shows the results of a quality resistance testconcerning resistance to a large crack forming in the circumferentialdirection in the rubber crawler track main body comparing the embodimentof the present invention and the conventional embodiment.

As quality resistance tests, the following two kinds of tests areperformed on the rubber crawler tracks from the fourth embodiment to thesixth embodiment and a rubber crawler track shown in FIG. 15 (aconventional embodiment 3) with a countermeasure for preventing a largecrack from occurring in the circumferential direction in the rubbercrawler track main body disclosed in Japanese Patent Laid-openPublication No. 079015 of 1999. The frequency that the depth of eachcrack of the following tests (1), (2) reaches 20 mm and the frequencythat the depth×the length thereof reaches 40 cm² are calculated from arelationship among the frequency of tests, the depth of a broken portionof the end portion (lug portion) of the rubber crawler track and thedepth×the length of the broken portion, and then, the frequencycalculated by making these frequencies in arithmetical mean is estimatedas the frequency of a large crack occurring in the circumferentialdirection in the rubber crawler track main body.

(1) A test for adding a load on an end portion (lug portion), wherein anoutside end portion (lug portion) of the rubber crawler track mounted ona hydraulic excavator is made to run aground on a curb, an arm of theexcavator is rotated 90 degrees to the traveling direction so as to belocated upward of the rubber crawler track, and then, the arm is made toshake from the upside to the downside and to suddenly stop before theexcavator contacts on the ground.

(2) A test for longitudinally reciprocating a hydraulic excavator whilemaking an outside end portion of a rubber crawler track of one side ofthe excavator run aground on boulders and maintaining this condition.

Obviously from Table 1, in comparison with that of the conventionalembodiment 3, the rubber crawler track of the fourth embodiment of thepresent invention has a twofold effect for quality resistance to a largecrack occurring in the circumferential direction in the rubber crawlertrack main body. Accordingly, a rubber crawler track for economicallyand effectively preventing a large crack from occurring in thecircumferential direction in the rubber crawler track main body can beprovided.

Besides, the rubber crawler track of the fifth embodiment of the presentinvention has almost equal quality resistance to the rubber crawler ofthe conventional embodiment 3 including core metal pieces whose endportions are bent to the inside circumferential side. Moreover, the coremetal piece shape of the fifth embodiment is simple in comparison withthat of the conventional embodiment 3. Therefore, a rubber crawler trackhaving good quality resistance to a large crack occurring in thecircumferential direction in the rubber crawler track main body can beprovided without cost.

Furthermore, the rubber crawler track of the sixth embodiment hasquality resistance to a large crack occurring in the circumferentialdirection in the rubber crawler track main body that is 2.7 times thatof the conventional embodiment.

In the present invention, in a rubber crawler track comprising coremetal pieces embedded in a rubber crawler track main body atpredetermined intervals in a circumferential direction of the rubbercrawler track, by interposing a high hardness intermediate rubber layerformed of a high hardness rubber elastic body having higher hardnessthan other rubber elastic bodies forming the rubber crawler track mainbody from below at least the ground contacting surface side of an endportion in a length direction of the core metal pieces toward outsidethe end portion in a width direction of the rubber crawler track, evenif the rubber crawler track runs aground on stones or curbs, rubber putbetween limbs of the core metal pieces and the stones or the curbs isprevented from being broken. Therefore, the occurrence of a large crackin the circumferential direction in the rubber crawler track main bodyis diminished, and the span of life of the rubber crawler track isprolonged.

The effect of the present invention can be accomplished by merelyadjusting rubber hardness of the rubber elastic body in the intermediaterubber layer. Therefore, the cost is not expensive, thereby economicallyand effectively preventing a large crack from occurring in thecircumferential direction in the rubber crawler track main body.

Besides, by improving the core metal pieces' shape, such as by makingthe ground contacting side of the end portion of a length direction ofthe core metal piece limb in a downward inclination within a fixedlength, destruction of the rubber between the core metal piece limb andthe stones or the curbs can be diminished. Therefore, the span of lifeof the rubber crawler track can be prolonged economically.

Moreover, by making thick a base rubber of the ground contacting surfaceside of the end portion in the crawler track width direction, includinga portion corresponding to the end portion of the core metal piece limb,the rigidity of the end portion of the rubber crawler track isincreased. Even if the rubber crawler track runs aground or is pushedagainst the stones or the curbs, the side end portion of the rubbercrawler track is difficult to bend to the inside circumference.Therefore, the occurrence of a large crack in the circumferentialdirection in the rubber crawler track main body is diminished and therigidity is improved.

1. A rubber crawler track, comprising: a rubber crawler track main bodyformed of a rubber elastic body; and core metal pieces embedded in saidrubber crawler track at predetermined intervals in a circumferentialdirection of the rubber crawler track, the core metal pieces having aground-facing side, wherein a high hardness intermediate rubber layerformed of a high hardness rubber elastic body is provided in said rubberelastic body from below at least the ground-facing side of an endportion of the core metal pieces, in a length direction of said coremetal pieces, to outside the end portion of the core metal pieces in awidth direction of the rubber crawler track, wherein a first portion ofthe high hardness intermediate rubber layer lies underneath an endportion of the core metal pieces in a length direction of the core metalpieces, a second portion of the high hardness intermediate rubber layerextends upward from said first portion and outside the end portion in awidth direction of the rubber crawler track, and said second portionadjoins said first portion, and wherein an upper portion of said rubberelastic body lies above said high hardness intermediate rubber layer, alower portion of said rubber elastic body lies below said high hardnessintermediate rubber layer, and said high hardness rubber elastic bodyhas higher hardness than both said upper and lower portions of saidrubber elastic body.
 2. A rubber crawler track as claimed in claim 1,wherein said end portion in the length direction of the core metalpieces is formed in a downward inclination having a fixed length.
 3. Arubber crawler track as claimed in claim 1, further comprising rubberlugs spaced from one another in the circumferential direction of therubber crawler track, wherein the thickness of an end portion of therubber crawler track, in a width direction of the rubber crawler track,is increased on the ground-facing side of the rubber crawler track toform a bulgy portion, and said bulgy portion is provided between rubberlugs in the circumferential direction of the rubber crawler track.